1. Field of Invention
The present invention relates to transimpedance amplifiers, and more particularly, to high-gain transimpedance amplifiers with reduced parasitic feedback and resonances.
2. Description of Related Art
A transimpedance amplifier is used to convert an input current to a proportional output voltage. A typical transimpedance amplifier comprises: an input current that is supplied through a transistor input stage, the input current is typically produced by a photodiode; an output carrying an output voltage; and a coupling member connecting the input to the output. Furthermore, the input current may be small, such as 1 μA, or comparatively large, such as 1 mA.
Typical uses of transimpedance amplifiers include summing currents as part of a frequency impulse response filter or processing reverse current produced by a photodiode as function of infrared signal energy received by the photodiode.
FIG. 1A illustrates a layout diagram 100 of a conventional high-gain transimpedance amplifier. Layout diagram 100 comprises: a power plane denoted 1; a group of one or more capacitors such as the block illustrated in diagram 100 denoted as 3; a group of one or more transistors such as the circuitry illustrated in diagram 100 denoted as 4; and a group of one or more pads such as the block illustrated in diagram 100 denoted as 5, wherein the group of one or more pads connecting power plane 1 to components adjacent to the amplifier.
However, conventional transimpedance amplifiers are composed almost entirely of metallic structures comprising material such as gold, aluminum, or copper. Therefore, use of resistive materials is restricted to resistors only. Such metallic geometries in layout and packaging may form parasitic feedback paths and resonances that may turn a high-gain transimpedance amplifier into an oscillator.
According, there is a need to include resistive layers in transimpedance amplifiers in order to reduce parasitic feedback and resonances.